It was a big hit. Cutesy robots. Beautiful animation. It even had an Al Gore-esque environmental message.

But the film also contained a darker, social commentary: a dystopian future where all humans had become obese. Too fat to walk, they roamed on padded hover-chairs, occupying their days with consumerism and over-consumption.

A fictional tale, yes. But is it really light years away from reality?

World Record Holders

You see, 21st-century humans are the fattest people that have ever walked the planet.

The World Health Organization1 estimates there are 1.9 billion overweight people in the world, 600 million of whom are obese. That’s a BMI of 30 or greater.

In 1980, the number of overweight people was less than half of that.

So, what has caused the recent epidemic?

Experts believe the answer is simple, if not easy to remedy.2 It’s just a simple matter of energy imbalance: we’re consuming more calories than we burn.

Part of this is because calories, at least in the West, have never been easier to come by. Energy dense processed foods–high in salt, sugar, and fat–have never been cheaper and more abundant.

Add into the mix increasingly office-bound, sedentary lifestyles–well you don’t have to be a rocket scientist to imagine the results.

So this isn’t exactly cutting-edge news. Even if we can’t help ourselves, we all know the dangers of eating too much crap and not exercising enough.

But what if the crisis of the world’s waistlines wasn’t just about food consumption? Might there be another reason for global obesity?

Well, it turns out there’s a growing body of evidence3 that suggests another possible causal factor for the obesity epidemic: the link betweenhow much people weigh and how much sleep they get.

Sleep: An Endangered Resource

Americans are getting less sleep than ever, according to data from the National Sleep Foundation.4 It’s not hard to believe.

Email and messaging extends our working day into the night. We binge on Netflix until the early hours, take our phones to sleep, and check Facebook under the bed covers. And we still get up for work at the regular time. Sleep in the 21st century has become marginalized.

Okay…But How is it Making me Fat?

Sleep deprivation has massive disruptive effects on health.5 The list of chronic conditions linked with poor quality sleep reads like a horror story. Diabetes, heart disease, Alzheimer’s, even some forms of cancer have been associated with poor sleep.

A recent review of scientific research6 on sleep and obesity found that short sleep duration is also linked to increased weight gain in a number of ways, including adverseeffects on appetite, physical activity, and body temperature.

The review looked at 31 publications from 1966 to 2007 and concluded that younger age groups were especially at risk of becoming overweight if they were identified as have a short sleep duration. Of all the causes, the review listed three potential mechanisms by which sleep deprivation can lead to obesity.

3 Reasons a Lack of Sleep is Making You Fat

1) Less sleep means greater opportunity to eat.

This might sound like it’s stating the obvious, but when you’re awake longer, you’ve got more time to eat, thus increasing your calorie intake.

A 2009 study concluded that “sleeping short hours in an obesity-promoting environment [i.e. your kitchen] may facilitate the excessive consumption of energy from snacks”.7

Think about it, when you’re into your 4th hour of Waking Dead at 3:00 AM, are you really going to put up much resistance to that lonely packet of Doritos lurking on the kitchen counter?

2) Disrupted sleep messes with your hunger hormones.

One of the results of disrupted sleep is that it plays havoc with your metabolic system. The circadian rhythm, our internal body clock, dictates not only the sleep/wake cycle, but also hormone production and appetite regulation.

Sleep deprivation turns out to have a double whammy effect on hunger and calorie consumption. Not only does sleep cause increased amounts of ghrelin, a hunger hormone (midnight munchies anyone?), but it also decreases the amount of leptin, the hormone that tells the brain that we’ve had enough to eat.

And if that’s not enough, studies8 have shown that sleep deprivation alters your brain chemistry to increase activity in the reward centers of the brain, making you more likely to crave unhealthy food and eat snacks.9

Basically, you’re screwed.

3) You’re too tired for physical activity.

Lastly, sleep plays an important regulatory role in energy expenditure. Simply speaking, if you’re sleep-deprived, you’re not likely to be very active, hence the calories burned part of the equation is going to decrease.

Again this might sound obvious, but another factor is thermoregulation, that is, maintaining your optimum body temperature. When you lack sleep, this can affect your core temperature, which in turn causes reduced energy expenditure and even more fatigue.

So, what can you do?

How can you benefit from knowing about the connection between sleep and obesity? Well, there are several things you can take away from the evidence.

If you’re up late and get the munchies, remember, you might not actually be hungry, it could just be your hormones out of whack. Try pouring yourself a glass of water.

If you work shifts or have trouble sleeping at night, try to compensate for sleep loss with strategic napping. This way, you’re less likely to suffer food cravings at weird times.

Most importantly you need to practice good sleep hygiene. This involves setting good sleep habits for yourself: a regular bedtime, plenty of natural light in the daytime, avoiding stimulants (coffee, alcohol, cigarettes) before bedtime, and banishing your gadgets from the bedroom.

About the Author

Hi, I’m Jeff, the founder and editor of Sleep Junkies, a sleep site for the 21st century. We cover all sleep-related topics from health, science, sleep hacks, to news, interviews and reviews of the latest cutting-edge sleep technology. We’ve attracted over a million other Sleep Junkies to our site. Our mission is simple. Sleep is god. Go worship. Follow our Twitter feed here.

In my understanding, when we lack sleep, our body thinks we are going to war and it's time to self-protect: absorb everything available and hold on to everything that is coming in. As a result, we eat more, burn less, and the body slows down the metabolism to ration the scares resources.